﻿/*
P Number 
Time Limit:1000MS  Memory Limit:32768K


Description:
Given a sequence b1, b2, b3… bn of odd length, the occurrence of every bi (i=1, 2, 3…n) is an even number except one number, 
the P number, which occurs odd times. Your task is to find that P number.

Input:
The input file contains several test case, each test case starts with a line contains an odd number n (0<n<10 000),
the length of the sequence, followed by a line with n numbers b1, b2, b3…bn.
It is guaranteed that every bi (i=1, 2, 3..,n) can be represented by a signed integer.
The input is terminated by a test case with n = 0. It should not be processed. 
Output:
For each test case, output a line the P number of the corresponding sequence. 
Sample Input:
5
2 3 2 3 4
7
2 2 2 2 2 2 2
0
Sample Output:
4
2
Hint:
O(n) algorithm exits. 
*/
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main()
{
	for (unsigned n; cin>>n && n;)
	{
		vector<unsigned> sequence;
		for (unsigned number; n--; sequence.push_back(number));
			cin>>number;

	}
	return EXIT_SUCCESS;
}